This invention relates to intravascular devices, and to methods of treatment using such devices.
Many forms of congenital heart disease result in shunting of the blood from the high resistance left-ventricle-aorta circuit into the low resistance right ventricle pulmonary artery circuit. This blood returns to the heart instead of going to the body and overloads the left ventricle causing congestion. This condition, known as congestive heart failure, is associated with difficulty in breathing and increased energy expenditure causing failure to thrive in the case of an infant. An additional and no less important aspect of such a shunt is the exposure of the lung blood vessels to high flow rates and pressures which eventually cause irreversible damage.
The solutions to the problems imposed by a large shunt include: medication to reduce the shunt, and repair of the heart defect by surgery of pulmonary artery banding [PAB]. This latter option, PAB, is employed today in cases when repair of the defect is not possible due to defect types or infant size or as a first stage palliative procedure for complex congenital disease.
PAB involves a surgical procedure under general anesthesia during which the chest is opened and a band of synthetic material is placed around the main pulmonary artery and tightened relatively arbitrarily to increase the resistance to flow. During the surgery pressures and oxygen saturation can be measured to evaluate the hemodynamic effect of banding however this does not always correlate well with findings after surgery. Apart from the general disadvantages of surgery [wound, scar, possibility of infection], surgical PAB can lead to distortion of the pulmonary arteries due to band migration. In addition if the band is too tight or loose it cannot be adjusted without additional surgery. Once the band has served it's purpose it has to be removed by surgery and the damaged area of the pulmonary artery is repaired. This is usually performed during the repair of the underlying defect.
The fields of cardiac catheterization and angiography have changed immensely with the introduction of transcatheter therapeutic/interventional techniques. It is now possible to close cardiac defects, relieve narrowings of systemic, pulmonary and coronary arteries, occlude accessory vessels, biopsy the heart and open valves through a small entry site, less than 2.5-3 mm, in the groin. These procedures obviate the need for surgery, including open heart, while affording excellent results. This minimally invasive approach avoids scarring and affords a more rapid recovery. The transcatheter procedure is usually performed on an overnight of same day basis thereby significantly reducing hospital stay and costs. A common example is the use of stents instead of bypass surgery in coronary artery stenosis.
An additional form of disease amenable to transcatheter therapy is pulmonary embolism. This condition is the result of blood clots which form in a vein of the lower part of the body and break loose, migrating to the lungs. One form of treatment of these emboli is by inserting a filter in a blood vessel such as the vena cava to interrupt the travel of these emboli. One such filter is disclosed in U.S. Pat. No. 4,425,908. Devices currently in use require relatively large sheaths for insertion, and are usually irretrievable.